Added AverageWindEncoder.

Refactored AverageWindDecoder - it now implements MessageDecoder.
Refactored AverageWind - it now uses milliseconds and knots, instead of packed MMperSec and tenths of a second. It also exposes its attributes now.
Added (un)packAverageWindPeriod to AC35UnitConverter.
Added AverageWindDecoderTest.
issue #35 #36
#story[1095]

racevisionGame/src/main/java/network/BinaryMessageDecoder.java

@@ -199,8 +199,8 @@ public class BinaryMessageDecoder {
 
             case AVGWIND:
                 //System.out.println("Average Wind Message!");
-                AverageWindDecoder awDecoder = new AverageWindDecoder(messageBody);
-                return awDecoder.getAverageWind();
+                AverageWindDecoder awDecoder = new AverageWindDecoder();
+                return awDecoder.decode(messageBody);
 
             case BOATACTION:
                 BoatActionDecoder baDecoder = new BoatActionDecoder();